Annals of botany最新文献

Background and aims: Aerenchyma formation has emerged as a promising model for understanding cell wall modifications. Certain cells undergo programmed cell death, whereas others do not, suggesting the existence of a tightly regulated signalling dispersion mechanism. Cell-to-cell communication occurs via plasmodesmata, whose permeability is regulated by the deposition of callose (β-1,3-glucan) and its degradation by β-1,3-glucanase. These processes might be key to understanding the selection of specific cells, which modify their cell walls for aerenchyma formation. Therefore, the aim of this study was to characterize the role of callose and β-1,3-glucanase during aerenchyma formation.

Methods: Sugarcane roots were segmented into five sections, each 1 cm in length, and embedded in LR White resin. Semi-thin sections were obtained, and immunolocalization was performed using monoclonal antibodies for the polysaccharides callose (β-1,3-glucan) and mixed-linkage β-1,3-1,4-glucan. The protein for in situ localization was chosen based on its ontology and protein domain structure. A super-resolution microscope was used to identify the antibody signal deposition pattern.

Key results: The antibody signal against mixed-linkage β-1,3-1,4-glucan was detected continuously along the cell wall in the early root segments. Its removal and degradation became evident from the third segment onwards, coinciding with aerenchyma formation. In contrast, callose exhibited a punctate signal, possibly marking regions of plasmodesmata. Callose degradation followed a similar pattern to that of mixed-linkage β-1,3-1,4-glucan (segment 3-segment 5), although its signal was less abundant. The β-1,3-glucanase showed peak signal from segment 3 to segment 4, accompanied by a punctate signal, suggesting its action at regions of plasmodesmata and callose degradation sites.

Conclusion: The presence of callose raises critical questions about how cells transmit signals and why only certain cells undergo programmed cell death. Managing the permeability and selectivity of intercellular communication might be a key factor in various biological processes. Gaining insight into these mechanisms and identifying potential enzymes and polysaccharides could provide new perspectives for future research.

Background and aims: Xylem and vessel structures help to maintain water transport in woody plants in response to environmental changes. Many studies have demonstrated the relationships between vessel structures and, in particular, temperature. However, the effects of environmental factors on the vessel size distribution and on vessels of different sizes have not been fully assessed statistically. Lianas are characterized by large vessels and vessel dimorphism. Liana abundance decreases with decreasing temperature; this pattern is attributed to the vulnerability of their large vessels to freeze-thaw embolism. However, in temperate zones, the relationships between liana abundance and temperature differ between twining and root climbers.

Methods: We sampled wood discs of eight liana species distributed across Japan and measured the size and shape of 130 940 vessels in 836 sections from 219 individuals. We classified vessels of each species into two diameter clusters (large and small) and calculated vessel traits and potential hydraulic conductivity (Kp). Vessel traits were compared among climbing mechanisms, and the relationships between vessel traits and temperature were analysed for species.

Key results: Twining climbers had larger vessel diameters than root climbers and had greater Kp. However, the relationships between temperature and vessel traits of species were inconsistent within climbing mechanisms. The decrease in Kp in certain species with decreasing temperature might result from species-specific changes in xylem structure. Vessels of the two clusters related differently to temperature in some species.

Conclusions: The vessel traits in each climbing mechanism might partly explain the distribution patterns of these lianas in the study region. Furthermore, changes in Kp in some species supported the prediction that liana competitiveness decreases with decreasing temperature. Understanding the mechanisms behind the changes in vessel traits and vessel size distribution along environmental factors will provide fundamental insights into how environmental changes affect forest ecosystems by altering plant hydraulic function.

Background and aims: Pollination by sexual deception is one of the most specialized pollination strategies among angiosperms, with co-occurring plant species often exploiting males of different insect species. We test if the morphologically divergent orchids Caladenia cardiochila and its sympatric endangered congener C. lowanensis are dependent on the same thynnine wasp pollinator. We further investigate the role of floral traits on pollinator behaviour and evaluate potential hybridization risk.

Methods: Pollinator sharing was tested for with DNA barcoding. Pollinator behaviour was quantified and experimental floral dissections were used to determine the site of sexual attractant release. We employed GC-MS to test for the presence of sugar on orchid labella, hand crosses to assess the impact of interspecific pollen transfer on seed viability, and population monitoring to quantify natural pollination success.

Key results: We found that C. cardiochila and C. lowanensis both employ sexual deception of Phymatothynnus aff. nitidus wasps as a pollination strategy. However, the behaviour they elicit differs, with wasps attempting to mate with the insectiform labellum in C. cardiochila and the glandular sepal tips in C. lowanensis, which are the respective sources of sexual attractant. Unlike most sexually deceptive orchids, C. lowanensis secretes minute amounts of sugar from its labellum. While wasps interacted more frequently with the labellum in C. cardiochila, placing them closer to its reproductive structures, both species exhibited comparable pollination success and pollen transfer efficiency. Experimental crosses revealed that hybrid seed has high viability.

Conclusions: Sexual deception of the same pollinator by orchids varying in the location of sexual attractant and flower morphology highlights the considerable flexibility of this pollination strategy. Given their overlapping distributions and the viability of hybrid seed, pollinator sharing poses a hybridization risk that needs to be considered in the management of wild C. lowanensis populations and future conservation translocations.

Background and aims: Antibiotics are natural compounds produced by microorganisms that have long existed in ecosystems. However, the widespread clinical and agricultural use of antibiotics has intensified selective pressures on bacteria, leading to the proliferation of antibiotic resistance genes (ARGs). The increasing prevalence of these genetic elements in clinical and environmental settings now poses a major global health threat. While ARGs are well documented in anthropogenically influenced environments, their distribution and origins in remote ecosystems, such as boreal forests, remain poorly understood. Here, we investigate the occurrence, diversity and potential origins of ARGs in the boreal lichen Cladonia stellaris.

Methods: We conducted the first targeted assessment of ARGs in lichens by analysing 42 C. stellaris samples from northern and southern lichen woodlands in eastern Canada. Using high-throughput quantitative PCR, we screened for 33 ARGs and three mobile genetic elements (MGEs), quantifying their relative abundance. Bacterial community composition was characterized via 16S rRNA gene sequencing. Statistical analyses evaluated geographical patterns, co-occurrence between ARGs and bacterial taxa, and the influence of latitude on ARG distribution.

Key results: Ten ARGs conferring resistance to four antibiotic classes (aminoglycosides, beta-lactams, quinolones and sulfonamides), along with one MGE, were detected. The ARGs blaCTX-M-1, qnrB and qepA were highly prevalent, with qepA often surpassing 16S rRNA gene abundance. Only qnrB showed significantly higher abundance in southern samples. Latitude significantly influenced ARG profiles, whereas bacterial community composition did not.

Conclusions: Our findings demonstrate that C. stellaris harbours diverse ARGs in remote boreal ecosystems with limited anthropogenic influence. Proposed explanations for ARG presence include long-distance dispersal via bioaerosols and endogenous development within lichen microbiomes, yet these remain speculative. Future work incorporating bacterial isolation, whole-genome sequencing, metatranscriptomics, air sampling and metabolomic profiling is necessary to unravel the ecology and evolution of ARGs in natural habitats.

Background and aims: Resource availability often limits female reproductive success in plants, especially when multiple flowers within inflorescences compete simultaneously for limited resources. Here, I explore whether relaxation of inter-ovary competition (through experimental thinning of inflorescences and/or inflorescence buds) influences resource allocation and enhances reproductive output in Lupinus polyphyllus, a legume species with vertical inflorescences that typically show a decline in fruit and seed production from basal to distal flowers.

Methods: I implemented a gradient of reproductive thinning: (1) no removal (control); (2) removal of half of the currently open inflorescences; and (3) removal of both half of the open inflorescences and all inflorescence buds (i.e. future racemes). For three randomly selected remaining inflorescences per plant, I recorded the total number of fruits within three sections along the inflorescence (basal, middle and distal). For each fruit in each of these three inflorescences, I also counted the number of viable seeds, aborted seeds and unfertilized ovules.

Key results: The results strongly supported the inter-ovary competition hypothesis. Inflorescence removal increased fruit and viable seed production and reduced seed abortion, especially when both inflorescences and buds were removed. These effects occurred consistently across all positions within inflorescences, suggesting enhanced resource allocation even to distal flowers, which are often resource limited. Ovule production per flower was unaffected, indicating no over-compensation prior to fertilization. The number of fertilized ovules declined from basal to distal flowers, consistent with non-uniform pollen receipt, probably influenced by bumblebee foraging behaviour. However, fertilization ratios remained high (80-90 %) across positions and treatments.

Conclusions: These findings demonstrate that inflorescence thinning can effectively relax resource-based constraints within and among inflorescences, enhancing female success without altering pollination dynamics. This contributes to our understanding of how architectural plasticity and developmental constraints shape reproductive trade-offs in flowering plants.

Background and aims: The capitulum of Asteraceae has traditionally been interpreted as a condensed raceme. However, morphological studies challenge this view, indicating that the capitulum does not arise from an inflorescence meristem, but from a determinate floral unit meristem. Terminology, combined with conflicting evidence from developmental genetics, has hindered the formulation of a coherent evolutionary scenario for the origin of the capitulum. In this paper, we aim to refine the floral unit concept and critically re-examine the hypothesis that ray flowers in Asteraceae represent remnants of ancestral thyrsoid branching.

Methods: Approaching from evolutionary-developmental morphology, we performed a detailed analysis of capitulum development in 20 highly diverse Asteraceae species, encompassing three subfamilies and 11 tribes, using scanning electron microscopy. We focused on early capitulum development, ray flower formation and changes in meristem geometry.

Key results: We show that the capitulum meristem is determinate and exhibits developmental features characteristic of flowers, thereby fulfilling the definition of a floral unit meristem. Continuous meristem expansion changes geometrical conditions and triggers spontaneous fractionation of flower meristems. The early developmental delay of ray flowers and the rare occurrence of bidirectional fractionation in the capitulum meristem can be explained morphologically by local expansion dynamics and mechanical pressure.

Conclusions: Our findings support the hypothesis that the capitulum meristem is distinct from an inflorescence meristem and instead recapitulates developmental properties of a flower meristem at a higher level of organization. This challenges the phylogenetic view that the capitulum evolved through gradual transformation of an ancestral thyrse. Instead, we propose that a single developmental shift (from an indeterminate reproductive meristem to a determinate floral unit meristem) was sufficient to give rise to the capitulum. The early determinacy of the meristem and the insertion of an additional step of fractionation are best explained by heterochronic changes, such as ontogenetic abbreviation and prolongation.

Background and aims: The maintenance of seed banks and timing of germination are fundamental to ensuring population persistence. Physical dormancy (PY) in disturbance-prone environments contributes to these processes via an impermeable seed coat. Dormancy is broken often by heating, which in fire-prone regions is determined by species-specific threshold temperatures. However, the mechanisms by which seeds persist or control dormancy-breaking thresholds in such environments are unclear. We determined whether unsaturated and saturated fatty acids (FAs; within triacylglycerols), common lipids linked to heat-stress resilience, might contribute to seed coat dormancy and overall seed persistence, and whether fire selects for different FA compositions and drives PY function in fire-prone regions.

Methods: We characterized seed FA compositions of 26 Fabaceae species from fire-prone and fire-free ecosystems through gas chromatography-mass spectrometry. We compared FA saturation, total relative FA content and the highest melting point FA of each species across seed tissues (seed coat vs internal tissues) and habitat type (fire-prone vs fire-free) and, for fire-prone species, tested for a relationship with species-specific dormancy-breaking thresholds.

Key results: No relationship between FA composition and species-specific dormancy-breaking thresholds was found. Seeds of fire-free species had more saturated FAs than fire-prone species, particularly for internal tissues. FA saturation was higher in seed coats than in internal tissues across both habitat types. Relative FA content was similar in internal tissues across habitat type but differed for seed coats, with fire-prone species having marginally more FAs.

Conclusions: While no correlation existed between FA composition and dormancy-breaking thresholds in fire-prone species, the consistent differences between seed tissue types we found highlight a similar role for FAs in seed coats across habitats, probably linked to maintaining impermeability. Some evidence supports fire selecting for greater total FA content in seed coats, but further work is needed to test its relationship with temperature thresholds.

Background and aims: Trait-based approaches have advanced our understanding of plant strategies; however, they often focus on leaf-level traits, overlooking the functional roles of stem anatomy and twig characteristics. We investigated intraspecific trait variation in Salix flabellaris, an alpine dwarf shrub, along climatic gradients in the Himalayas. Our goal was to identify distinct axes of trait variation related to stem, twig and leaf traits, assess their environmental drivers and evaluate population-specific growth responses to recent climate change.

Methods: We measured anatomical and morphological traits in stems, twigs and leaves across central and marginal populations along three Himalayan transects. Environmental gradients included variation in growing season temperature and soil moisture. Basal area increment from 2000 to 2021 was analysed to assess long-term growth trends in different areas.

Results: Trait dimensions were largely independent, reflecting distinct ecological strategies: (1) stem anatomical trade-off between hydraulic safety and conductivity; (2) twig dimension balancing construction costs and mechanical strength; and (3) leaf dimension along the exploitative-conservative axis. Higher temperatures enhanced performance, manifested as larger twigs and reduced tissue construction costs, but only in conditions with sufficient soil moisture. Central populations at mid-elevations displayed the favourable trait combinations and highest growth rates. In contrast, marginal populations (higher and lower elevations) showed traits indicating structural reinforcement and conservative resource use. Climate warming over recent decades enhanced stem growth primarily in high-elevation populations, where low-temperature constraints were relaxed.

Conclusions: This study demonstrates that stem, twig and leaf traits represent distinct yet complementary strategies, with environmental filtering shaping their expression along climate gradients. Central populations exhibit the highest growth in current conditions, and climate change is shifting growth advantages towards higher elevations. These findings highlight the need for integrated, multi-organ trait assessments to predict species performance, persistence and potential range shifts under future climatic scenarios.

Background and aims: Automatized species identification tools have massively facilitated plant identification. In mosses, spore ultrastructure appears to be a promising taxonomic character, but has been largely under-exploited. Here, we test artificial intelligence-based approaches to identify species from their spore morphology. In particular, we determine whether the number of spores, their polarity, and variation among populations and capsules affect model accuracy.

Methods: Scanning electron microscopy spore images were generated for five capsules of five populations in ten species. Convolutional neural networks with a highly modularized architecture (ResNeXt) were trained to identify the species, population and capsule of origin of a spore. The training set was progressively sub-sampled to test the impact of sample size on model accuracy. To assess whether variation in spore morphology among populations affected model accuracy, one population was successively removed to test a model trained on the four remaining populations.

Key results: Species were correctly identified at average rates of 92 %, regardless of polarity. Model accuracy decreased progressively with decreasing sample size, dropping to about 80 % with 15 % of the initial dataset. The population and capsule of origin of a spore was retrieved at rates >75 %, indicating the presence of diagnostic population and capsule markers on the sporoderm. Strong population structure in some species caused a substantial drop of model accuracy when model training and testing was performed on different populations.

Conclusions: Spore morphology appears to be an extremely promising tool for moss species identification and may usefully complement the suite of morphological characters used so far in moss taxonomy. The presence of spore diagnostic features at the population and capsule level raises substantial questions on the origin of this structure, which are discussed. Substantial infraspecific variation makes it necessary, however, to train an automatized identification tool from a range of populations and capsules.